Showing papers in "Ecological Monographs in 2006"
TL;DR: Common scales of shade, drought, and waterlogging tolerance for 806 North American, European/West Asian, and East Asian temperate shrubs and trees were constructed to test the hypotheses that shade tolerance is negatively related to drought andWaterlogging tolerances, and that these correlations vary among continents and plant functional types.
Abstract: Lack of information on ecological characteristics of species across different continents hinders development of general world-scale quantitative vegetation dynamic models. We constructed common scales of shade, drought, and waterlogging tolerance for 806 North American, European/West Asian, and East Asian temperate shrubs and trees representing about 40% of the extant natural Northern Hemisphere species pool. These scales were used to test the hypotheses that shade tolerance is negatively related to drought and waterlogging tolerances, and that these correlations vary among continents and plant functional types. We observed significant negative correlations among shade and drought tolerance rankings for all data pooled, and separately for every continent and plant functional type, except for evergreen angiosperms. Another significant trade-off was found for drought and waterlogging tolerance for all continents, and for evergreen and deciduous angiosperms, but not for gymnosperms. For all data pooled, for Europe and East Asia, and for evergreen and deciduous angiosperms, shade tolerance was also negatively associated with waterlogging tolerance. Quantile regressions revealed that the negative relationship between shade and drought tolerance was significant for species growing in deep to moderate shade and that the negative relationship between shade and waterlogging tolerance was significant for species growing in moderate shade to high light, explaining why all relationships between different tolerances were negative according to general regression analyses. Phylogenetic signal in the tolerance to any one of the three environmental factors studied was significant but low, with only 21-24% of cladogram nodes exhibiting significant conservatism. The inverse relationships between different tolerances were significant in phylogenetically independent analyses both for the overall pool of species and for two multispecies genera (Pinus and Quercus) for which reliable molecular phylogenies were available. Only 2.6-10.3% of the species were relatively tolerant to two environmental stresses simultaneously (tolerance value � 3), and only three species were tolerant to all three stresses, supporting the existence of functional trade-offs in adjusting to multiple environmental limitations. These trade-offs represent a constraint for niche differentiation, reducing the diversity of plant responses to the many combinations of irradiance and water supply that are found in natural ecosystems.
950 citations
TL;DR: This guild-based decomposition model (GDM) includes the interactions of holocellulose and lignin, manifest as mutual feedback controls on microbial-based activities, and includes N limitations on early stages of litter decay resulting from nutritional demands of microorganisms and N inhibition on late stages of pollution-induced degradation.
Abstract: Despite the central role of microorganisms in the decomposition of dead organic matter, few models have integrated the dynamics of litter chemistry with microbial interactions. Here we propose a functional resolution of the microbial community that parallels the commonly used chemical characterization of plant litter, i.e., a guild of opportunist microorganisms that grows quickly and has high affinity for soluble substrates, a guild of decomposer specialists that grows more slowly and has high affinity for holocellulose substrates, and a guild of miners that grows very slowly and is specialized for degrading lignin. This guild-based decomposition model (GDM) includes the interactions of holocellulose and lignin, manifest as mutual feedback controls on microbial-based activities. It also includes N limitations on early stages of litter decay resulting from nutritional demands of microorganisms and N inhibition on late stages of litter decay resulting from reduced lignin degradation. Competitive interaction...
721 citations
TL;DR: This study is the first to identify specific life-history strategies that are associated with extensive range reduction of native species and expansion of nonnative species, and it highlights the utility of using niche and life- history perspectives to evaluate different mechanisms that contribute to the patterns of fish invasions and extirpations in the American Southwest.
Abstract: Understanding the mechanisms by which nonnative species successfully in- vade new regions and the consequences for native fauna is a pressing ecological issue, and one for which niche theory can play an important role In this paper, we quantify a com- prehensive suite of morphological, behavioral, physiological, trophic, and life-history traits for the entire fish species pool in the Colorado River Basin to explore a number of hypotheses regarding linkages between human-induced environmental change, the creation and mod- ification of ecological niche opportunities, and subsequent invasion and extirpation of species over the past 150 years Specifically, we use the fish life-history model of K O Winemiller and K A Rose to quantitatively evaluate how the rates of nonnative species spread and native species range contraction reflect the interplay between overlapping life- history strategies and an anthropogenically altered adaptive landscape Our results reveal a number of intriguing findings First, nonnative species are located throughout the adaptive surface defined by the life-history attributes, and they surround the ecological niche volume represented by the native fish species pool Second, native species that show the greatest distributional declines are separated into those exhibiting strong life-history overlap with nonnative species (evidence for biotic interactions) and those having a periodic strategy that is not well adapted to present-day modified environmental conditions Third, rapidly spreading nonnative fishes generally occupy ''vacant'' niche positions in life-history space, which is associated either with ''niche opportunities'' provided by human-created envi- ronmental conditions (consistent with the environmental-resistance hypothesis of invasion) or with minimal overlap with native life-history strategies (consistent with the biotic- resistance hypothesis) This study is the first to identify specific life-history strategies that are associated with extensive range reduction of native species and expansion of nonnative species, and it highlights the utility of using niche and life-history perspectives to evaluate different mechanisms that contribute to the patterns of fish invasions and extirpations in the American Southwest
450 citations
TL;DR: In this article, the authors quantified spatial and temporal patterns in the body temperature of an ecologically important species of intertidal invertebrate, the mussel Mytilus californianus, along the majority of its latitudinal range from Washington to southern California, USA.
Abstract: We explicitly quantified spatial and temporal patterns in the body temperature of an ecologically important species of intertidal invertebrate, the mussel Mytilus californianus, along the majority of its latitudinal range from Washington to southern California, USA. Using long-term (five years), high-frequency temperature records recorded at multiple sites, we tested the hypothesis that local ''modifying factors'' such as the timing of low tide in summer can lead to large-scale geographic mosaics of body temperature. Our results show that patterns of body temperature during aerial exposure at low tide vary in physiologically meaningful and often counterintuitive ways over large sections of this species' geographic range. We evaluated the spatial correlations among sites to explore how body temperatures change along the latitudinal gradient, and these analyses show that ''hot spots'' and ''cold spots'' exist where temperatures are hotter or colder than expected based on latitude. We identified four major hot spots and four cold spots along the entire geographic gradient with at least one hot spot and one cold spot in each of the three regions examined (Washington- Oregon, Central California, and Southern California). Temporal autocorrelation analysis of year-to-year consistency and temporal predictability in the mussel body temperatures revealed that southern animals experience higher levels of predictability in thermal signals than northern animals. We also explored the role of wave splash at a subset of sites and found that, while average daily temperature extremes varied between sites with different levels of wave splash, yearly extreme temperatures were often similar, as were patterns of predictability. Our results suggest that regional patterns of tidal regime and local pattern of wave splash can overwhelm those of large-scale climate in driving patterns of body temperature, leading to complex thermal mosaics of temperature rather than simple latitudinal gradients. A narrow focus on population changes only at range margins may overlook climatically forced local extinctions and other population changes at sites well within a species range. Our results emphasize the importance of quantitatively examining biogeographic patterns in environ- mental variables at scales relevant to organisms, and in forecasting the impacts of changes in climate across species ranges.
436 citations
TL;DR: In this paper, the authors describe a discrete-time, stochastic population model with density dependence, environmental-type process noise, and lognormal observation or sampling error.
Abstract: We describe a discrete-time, stochastic population model with density depend ence, environmental-type process noise, and lognormal observation or sampling error. The model, a stochastic version of the Gompertz model, can be transformed into a linear Gaussian state-space model (Kaiman filter) for convenient fitting to time series data. The model has a multivariate normal likelihood function and is simple enough for a variety of uses ranging from theoretical study of parameter estimation issues to routine data analyses in population monitoring. A special case of the model is the discrete-time, stochastic exponential growth model (density independence) with environmental-type process error and lognormal observation error. We describe two methods for estimating parameters in the Gompertz state-space model, and we compare the statistical qualities of the methods with computer simulations. The methods are maximum likelihood based on observations and restricted maximum likelihood based on first differences. Both offer adequate statistical properties. Because the likelihood function is identical to a repeated-measures analysis of variance model with a random time effect, parameter estimates can be calculated using PROC MIXED of SAS. We use the model to analyze a data set from the Breeding Bird Survey. The fitted model suggests that over 70% of the noise in the population's growth rate is due to observation error. The model describes the autocovariance properties of the data especially well. While observation error and process noise variance parameters can both be estimated from one time series, multimodal likelihood functions can and do occur. For data arising from the model, the statistically consistent parameter estimates do not necessarily correspond to the global maximum in the likelihood function. Maximization, simulation, and bootstrapping programs must accommodate the phenomenon of multimodal likelihood functions to produce statistically valid results.
409 citations
TL;DR: The results suggest that tissue structure and longevity aboveground (leaves) can contrast markedly with that belowground (roots), which corroborates previous research that has suggested a trade-off between organ life span and higher organ N concentrations.
Abstract: Global data sets provide strong evidence of convergence for leaf structure with leaf longevity such that species having thick leaves, low specific leaf area, low mass-based nitrogen concentrations, and low photosynthetic rates typically exhibit long leaf life span. Leaf longevity and corresponding leaf structure have also been widely linked to plant potential growth rate, plant competition, and nutrient cycling. We hypothesized that selection forces leading to variation in leaf longevity and leaf structure have acted simultaneously and in similar directions on the longevity and structure of the finest root orders. Our four-year study investigated the links between root and leaf life span and root and leaf structure among 11 north-temperate tree species in a common garden in central Poland. Study species included the hardwoods Acer pseudoplatanus L., Acer platanoides L., Fagus sylvatica L., Quercus robur L., and Tilia cordata Mill.; and the conifers Abies alba Mill., Larix decidua Mill., Picea abies (L.) Karst., Pinus nigra Arnold, Pinus sylvestris L., and Pseudotsuga menziesii (Mirbel) Franco. Leaf life span, estimated by phenological observations and needle cohort measurements, ranged from 0.5 to 8 yr among species. Median fine-root life span, estimated using minirhizotron images of individual roots, ranged from 0.5 to 2.5 yr among species. Root life span was not correlated with leaf life span, but specific root length was significantly correlated with specific leaf area. Root nitrogen : carbon ratio was negatively correlated with root longevity, which corroborates previous research that has suggested a trade-off between organ life span and higher organ N concentrations. Specific traits such as thickened outer tangential walls of the exodermis were better predictors of long-lived roots than tissue density or specific root length, which have been correlated with life span in previous studies. Although theories linking organ structure and function suggest that similar root and leaf traits should be linked to life span and that root and leaf life span should be positively correlated, our results suggest that tissue structure and longevity aboveground (leaves) can contrast markedly with that belowground (roots).
409 citations
TL;DR: In this article, the Ecological Society of America (ESA) have published a survey of the state of the art in the field of ecology and evolutionary biology, with a focus on watershed management.
Abstract: Copyright by the Ecological Society of America 2006, for personal or educational use only. Article is available at
318 citations
TL;DR: Although suppression was the dominant demographic process, mechanical damage yielded greater loss of biomass and greater structural heterogeneity through creation of windthrow gaps, suggesting gap-forming processes that operate late in succession and contribute to structural complexity in old-growth forests can also occur early in stand development.
Abstract: Tree mortality is a critical but understudied process in coniferous forest development. Current successional models assume that mortality during early forest development is dominated by density-dependent processes, but few long-term studies exist to test this assumption. We examined changes in forest structure and patterns of tree mortality 14-38 years (1979-2001) after clear-cut logging of two experimental watersheds in the western Cascade Range of Oregon, USA. We sampled 193 permanent plots (250 m 2 ) six times generating 75 126 data records and 7146 incidents of mortality. Mean density peaked at .3000 stems/ha (� 1.4 m tall) after 22-25 years; bole biomass increased continuously to .100 Mg/ha. At final sampling, stem density varied by two orders of magnitude and biomass by a factor of 10 among sample plots. Suppression mortality occurred in .80% of plots and was .2.5 times as frequent as mechanical damage (uprooting, stem snap, and crushing). However, biomass lost to mortality via mechanical damage was nearly four times that lost to suppression, a result of episodic storms that created windthrow patches, with some plots losing 30-50% of biomass. Total annual mortality increased from 1.0% to 5.3% of stems over the study period and was highly variable among species. Although mortality rates were highest for sprouting hardwoods (reaching 9.7% in Cornus nuttallii), biomass of most hardwood species increased through canopy closure as dominant stems achieved large sizes. Shade-tolerant conifers (Tsuga heterophylla and Thuja plicata), typically assumed to be absent or to play a minor role in early forest development, accounted for 26% of stems after 38 years. In regression tree models, environmental attributes of plots had limited ability to predict mortality. Instead, stem density prior to canopy closure was the strongest predictor of cumulative mortality (either suppression or mechanical damage). Our long-term studies suggest that current models of early forest development are overly simplistic, particularly in their treatment of mortality. Although suppression was the dominant demographic process, mechanical damage yielded greater loss of biomass and greater structural heterogeneity through creation of windthrow gaps. Thus, gap-forming processes that operate late in succession and contribute to structural complexity in old-growth forests can also occur early in stand development.
215 citations
TL;DR: It is argued that sexual recruitment is more prevalent in the eastern range of A. palmata than the west, and that these geographic differences in the contribution of reproductive modes to population structure may be related to habitat characteristics.
Abstract: Species that build the physical structure of ecosystems often reproduce clonally, both in terrestrial (e.g., grasses, trees) and marine (e.g., corals, seagrasses) environments. The degree of clonality may vary over a species' range in accordance with the relative success of sexual and asexual recruitment. High genotypic (clonal) diversity of structural species may promote the species diversity and resilience of ecosystems in the face of environmental extremes. Conversely, low genotypic diversity may indicate an asexual strategy to maintain resources and genetic variation during population decline. Here, we use microsatellite markers to assess geographic variation in clonality in the coral Acropora palmata sampled from 26 reefs in eight regions spanning its tropical western Atlantic range (n ¼ 751). Caribbean-wide, the ratio (6SD) of genets (Ng) to sampled ramets (N) was 0.51 6 0.28. Within reefs (30-70 m) and among reefs (10-100 km) within regions, clonal structure varied from being predominantly asexual (Ng/N approaching 0) to purely sexual (Ng/N ¼ 1). However, two genetically isolated regions (western and eastern Caribbean) differed in clonal structure: genotypically depauperate populations (Ng/N ¼ 0.43 6 0.31) with lower densities (0.13 6 0.08 colonies/m 2 ) characterized the western region, while denser (0.30 6 0.21 colonies/m 2 ), genotypically rich stands (Ng/N ¼ 0.64 6 0.17) typified the eastern Caribbean. Genotypic richness (standardized to sample size; Ng/N) and genotypic diversity (Go/Ge) were negatively related to colony density within each province (r 2 ¼ 0.49-0.66, P , 0.001), indicating that dense stands have higher rates of asexual recruitment than less dense populations. Asexual recruitment was not correlated with large- scale disturbance history or abundance of large colonies (potential fragment sources) but was negatively correlated with shelf area (r 2 ¼ 0.57, P , 0.01). We argue that sexual recruitment is more prevalent in the eastern range of A. palmata than the west, and that these geographic differences in the contribution of reproductive modes to population structure may be related to habitat characteristics. The two populations of the threatened A. palmata differ fundamentally in reproductive character and may respond differently to environmental change.
202 citations
TL;DR: The results suggest that stable coexistence mediated by competition for phosphorus and light is rare, and hence an unlikely explanation for the high biodiversity commonly found in phytoplankton communities.
Abstract: Competition theory has put forward three contrasting hypotheses: Compe- tition for nutrients and light may lead to (i) stable coexistence of species, (ii) alternative stable states, or (iii) competitive exclusion. This paper presents a detailed investigation of competition among phytoplankton species to test these three different hypotheses. First, we developed a competition model combining competition for nutrients and light. Next, we ran monoculture experiments in phosphorus-limited and light-limited chemostats to estimate the model parameters for five freshwater phytoplankton species. Finally, we tested the model predictions in competition experiments, using phosphorus levels ranging from oligotrophic to eutrophic conditions. The population dynamics in the competition experi- ments were all in agreement with the model predictions. This demonstrates that competition for nutrients and light can be accurately predicted over a wide range of productivities. The experiments revealed that the intensity of competition remained constant or even decreased with increasing nutrient supply. Contrary to expectation, there were no trade-offs between competitive abilities for phosphorus and light. Species that were strong competitors for phosphorus were strong competitors for light as well. Hence, we found neither stable coexistence nor alternative stable states. All competition experiments led to competitive exclusion. Furthermore, the physiological traits of the species indicated that, if one would find trade-offs in competitive abilities, competition for phosphorus and light would lead to alternative stable states rather than to stable coexistence. These results suggest that stable coexistence mediated by competition for phosphorus and light is rare, and hence an unlikely explanation for the high biodiversity commonly found in phytoplankton communities.
201 citations
TL;DR: How the introduction of foxes onto the Aleutian Islands transformed plant communities by reducing abundant seabird populations, thereby disrupting nutrient sub- sidies vectored by seabirds from sea to land is quantified.
Abstract: The ramifying effects of top predators on food webs traditionally have been studied within the framework of trophic cascades. Trophic cascades are compelling because they embody powerful indirect effects of predators on primary production. Although less studied, indirect effects of predators may occur via routes that are not exclusively trophic. We quantified how the introduction of foxes onto the Aleutian Islands transformed plant communities by reducing abundant seabird populations, thereby disrupting nutrient sub- sidies vectored by seabirds from sea to land. We compared soil and plant fertility, plant biomass and community composition, and stable isotopes of nitrogen in soil, plants, and other organisms on nine fox-infested and nine historically fox-free islands across the Aleu- tians. Additionally, we experimentally augmented nutrients on a fox-infested island to test whether differences in plant productivity and composition between fox-infested and fox- free islands could have arisen from differences in nutrient inputs between island types. Islands with historical fox infestations had soils low in phosphorus and nitrogen and plants low in tissue nitrogen. Soils, plants, slugs, flies, spiders, and bird droppings on these islands had low d 15 N values indicating that these organisms obtained nitrogen from internally derived sources. In contrast, soils, plants, and higher trophic level organisms on fox-free islands had elevated d 15 N signatures indicating that they utilized nutrients derived from the marine environment. Furthermore, soil phosphorus (but not nitrogen) and plant tissue ni- trogen were higher on fox-free than fox-infested islands. Nutrient subsidized fox-free islands supported lush, high biomass plant communities dominated by graminoids. Fox-infested islands were less graminoid dominated and had higher cover and biomass of low-lying forbs and dwarf shrubs. While d 15 N profiles of soils and plants and graminoid biomass varied with island size and distance from shore, after accounting for these effects differences between fox-infested and fox-free islands still existed. Fertilization over four years caused a 24-fold increase in graminoid biomass and a shift toward a more graminoid dominated plant community typical of fox-free islands. These results indicate that apex predators can influence plant productivity and composition through complex interaction web pathways involving both top-down forcing and bottom-up nutrient exchanges across systems.
TL;DR: In this paper, the authors measured endemic and total richness and environmental variables in 109 serpentine sites (1000-m 2 paired plots) in 78 serpentine-containing regions of the state and used structural equation modeling (SEM) to simultaneously relate regional richness to regional scale predictors, and local richness to both local-scale and regional-scale predictors.
Abstract: We asked how the richness of the specialized (endemic) flora of serpentine rock outcrops in California varies at both the regional and local scales. Our study had two goals: first, to test whether endemic richness is affected by spatial habitat structure (e.g., regional serpentine area, local serpentine outcrop area, regional and local measures of outcrop isolation), and second, to conduct this test in the context of a broader assessment of environmental influences (e.g., climate, soils, vegetation, disturbance) and historical influences (e.g., geologic age, geographic province) on local and regional species richness. We measured endemic and total richness and environmental variables in 109 serpentine sites (1000-m 2 paired plots) in 78 serpentine-containing regions of the state. We used structural equation modeling (SEM) to simultaneously relate regional richness to regional- scale predictors, and local richness to both local-scale and regional-scale predictors. Our model for serpentine endemics explained 66% of the variation in local endemic richness based on local environment (vegetation, soils, rock cover) and on regional endemic richness. It explained 73% of the variation in regional endemic richness based on regional environment (climate and productivity), historical factors (geologic age and geographic province), and spatial structure (regional total area of serpentine, the only significant spatial variable in our analysis). We did not find a strong influence of spatial structure on species richness. However, we were able to distinguish local vs. regional influences on species richness to a novel extent, despite the existence of correlations between local and regional conditions.
TL;DR: Patagonian rocky shore communities are exposed to unusually harsh physical conditions and consequently are more strongly organized by physical stress than previously studied rocky intertidal communities.
Abstract: We examined the structure of rocky intertidal communities on the central Patagonian coast of Argentina. Extensive beds of the mussel Perumytilus purpuratus cover wave-exposed headlands from the low to extreme high intertidal (>95%), and a diverse assemblage of diminutive mobile invertebrates including limpets, starfish, and crabs live exclusively in the mussel bed matrix to avoid physical stress. On nearby wave-protected rocky shores, the high intertidal habitat is dominated by bare space (>85%) with mussels restricted to tide pools and crevices. Mussel beds cover the middle intertidal, while the low intertidal habitat is dominated by the erect coralline alga Corallina officanalis. These patterns are driven overwhelmingly by variation in extreme physical conditions. Desiccation stress generated by the dry southern trade winds is harsher than in any previously studied rocky intertidal system, including the Gulf of Panama, by >30% and is more severe on wave-protected than wave-exposed shores. Transplant experiments suggest that on wave-protected shores desiccation stress limits the upper distribution of mussels in the high intertidal and Corallina in the mid-intertidal, but at low intertidal elevations Corallina outcompetes mussels, restricting mussel distribution to mid-intertidal elevations. Transplant experiments also demonstrated that the coralline alga is precluded from wave-exposed shores by wave stress. Recovery from disturbance is unusually slow, ostensibly due to extreme physical stress. Consumer pressure is weak, with no common predaceous crabs or snails, and grazing by limpets showed limited control of community development, mostly by regulating ephemeral algae. Patagonian rocky shore communities are exposed to unusually harsh physical conditions and consequently are more strongly organized by physical stress than previously studied rocky intertidal communities.
TL;DR: The hypothesis was that successively modifying the factors influencing the causes of succession in an integrated fashion would favor the establishment and abundance of native grasses over singularly applied treatments and the majority of responses to multiple treatments would be explained by higher order interactions.
Abstract: Ecologists are searching for models, frameworks, and principles that provide a bridge between theory and the practice of restoration. Successional management has been proposed as a useful model for managing and restoring invasive-plant-dominated rangeland because it provides a framework in which ecological processes can be manipulated by managers to achieve a desired plant community. Successional management identifies three general causes of succession (site availability (disturbance), species availability (colonization), and species performance) and suggests that managers address the ecological process influencing each general cause in a coordinated fashion to direct plant community dynamics. We tested successional management using various techniques to restore invasive-weed-dominated rangeland. Our hypothesis was that successively modifying the factors influencing the causes of succession in an integrated fashion would favor the establishment and abundance of native grasses over singularly applied treatments. Thus, we anticipated that the majority of responses to multiple treatments would be explained by higher order interactions, especially in the final year of the study (2004). To test this hypothesis, we used a model system within a Festuca campestris/Pseudoroegneria spicata habitat among pothole wetlands dominated by Centaurea maculosa and Potentilla recta, two invasive species. We used three herbicide treatments (none, 2,4-D, and picloram) to influence species performance; two seeding methods (imprinting, i.e., creating a small depression and broadcasting, and no-till drilling) to influence disturbance; three seeding rates (977, 1322, and 1557 seeds/m 2 ) to influence colonization; and two cover crop treatments (with and without Triticum aestivum) to influence soil N and favor native grasses. Treatments were factorially arranged and replicated four times in a randomized complete block design in 2001 and sampled in 2002 and 2004. As predicted, plant response to treatments was dominated by two- and three-way interactions in 2004. The highest seeding rate (colonization) combined with no-till drilling (disturbance) produced the highest native grass density in 2002. These effects persisted into 2004 for P. spicata, but not for F. campestris or F. idahoensis. Combining picloram with no-till drill seeding also produced a high density of P. spicata. Drill seeding at 977 seeds/m 2 favored F. idahoensis density, while no-till drilling at 1322 seeds/m 2 favored its biomass in 2004. F. idahoensis established well after drill seeding with a cover crop and applying 2,4-D. Herbicides reduced native forb density and/or biomass, with early season forbs being more sensitive to picloram and summer forbs being more sensitive to 2,4-D. Herbicides increased exotic grasses' density and biomass but had no effect on native grasses. In most cases, integrating treatments that addressed multiple causes of succession favored a desired plant community. Thus, we accomplished our goal of using successional management to direct plant communities toward native desired species, but the treatments used did not improve species richness. Since naturally occurring native forbs did not respond favorably to any treatment combination, ecological restoration using successional management may best be thought of as an iterative procedure where various components and processes of the system are methodically repaired or replaced over time.
TL;DR: Changes in population abundance within this multi-prey, generalist predator system arose from a complex interplay between changing climatic conditions, variable food production, shifting habitat conditions, varying vulnerability to predation, and spillover effects on other species.
Abstract: The dynamics of animal populations can be influenced directly by prevailing resources, population density, and environmental conditions, and through the delayed effects of trophic interactions and abiotic effects on habitat conditions. For large mammals, lagged effects can extend several years back in time. We attempted to establish the causal processes governing the population changes shown by 11 ungulate species counted annually over a 20-year period in South Africa's Kruger National Park. Kudu, waterbuck, warthog, sable, tsessebe, roan, and eland declined progressively in abundance after 1986, while zebra, wildebeest, impala, and giraffe maintained high abundance levels. To identify lagged influences, we used statistical probes indexing (1) inferred changes in predator abundance as a consequence of past food availability, (2) effects on habitat conditions of prior rainfall, and (3) competitor impacts on shared food resources. Multiple linear regression models were fit to estimates of annual population growth derived from the count totals subdivided among four regions. The temporal pattern of the population declines by five species was most consistent with a lagged effect from past predator food, in addition to the direct effects of seasonal rainfall. However, models including the lagged effect of prior rainfall fit nearly as well. Species that maintained high abundance responded mainly to an immediate or lagged density feedback. Changing rainfall conditions apparently affect the relative susceptibility of ungulate species to predation. Hence, the top-down interaction with predators cannot readily be disentangled from extrinsic influences on population dynamics, mediated through resources. Population declines by some species became extreme because a prolonged period of low rainfall, especially in the dry-season component, followed a doubling in the food base supporting lions, and was coupled with widened prey distribution as a consequence of the augmentation of water points by managers. Changes in population abundance within this multi-prey, generalist predator system arose from a complex interplay between changing climatic conditions, variable food production, shifting habitat conditions, varying vulnerability to predation, and spillover effects on other species.
TL;DR: A combination of theoretical and experimental approaches are used to examine spore dispersal in Macrocystis, where complex coastal flows affect self-fertilization and inbreeding depression near to a source, as well as propagule delivery dictating recovery of locally extinct populations farther away.
Abstract: Passively dispersing propagules are often transported across a range of scales, with impacts on local processes tied to the density of settlement, and on regional processes influencing population connectivity. This dual set of effects has spurred research targeting both short- and long-distance ends of the dispersal spectrum. To date, however, dispersal distributions have been rigorously quantified primarily in terrestrial plants with seeds. Dispersal distributions in the ocean are by comparison poorly defined. This limitation arises with particular force in the habitat-forming giant kelp, Macrocystis pyrifera, where complex coastal flows affect self-fertilization and inbreeding depression near to a source, as well as propagule delivery dictating recovery of locally extinct populations farther away. Here we use a combination of theoretical and experimental approaches to examine spore dispersal in Macrocystis. Results from a physically based model, parameterized via field-measured hydrodynamics, are compar...
TL;DR: A vegetation chronosequence spanning over 300 years was established in unconstrained reaches of the lower Queets River in Olympic National Park, Washington, USA, for an examination of riparian successional patterns as mentioned in this paper.
Abstract: A vegetation chronosequence spanning over 300 years was established in unconstrained reaches of the lower Queets River in Olympic National Park, Washington, USA, for an examination of riparian successional patterns. The Queets is an unconstrained, dynamic, mountain river located within a temperate rain forest environment. Ongoing chan- nel movements create intricate patterns in the physical structure of the valley. Twenty-one plots containing a total of 4359 trees were mapped and measured for structural and crown characteristics. Snags, logs, and understory vegetation were also quantified. Recent alluvial deposits are colonized primarily by early-successional trees Salix sitchensisand Alnus rubra. Conifer seedlings, primarily Picea sitchensis, generally invade after the initial cohort of hardwood trees begins senescence: 20-30 years for Salix and 40-60 years for Alnus. Through accumulation of sediments from floods and channel downcutting, surfaces become perched above the reach of annual floods after 40-80 years and are then slowly colonized by late successional tree species Acer circinatum, Acer macrophyllum, and Tsuga hetero- phylla. Diverse, old-growth forests ultimately develop after 200-250 years, containing some of the largest known trees in the Pacific Northwest. However, canopy and stem densities remain lower than comparative Pseudotsuga menziesii forests from the nearby Cascade Mountains. Vast individual crowns can develop, with occasional Picea up to 25 m wide and 70 m deep. Individual stands may accumulate .200 000 m 3 /ha of canopy volume— among the highest recorded on earth. Mixed among the generalized successional sequence are variations created by uncommon channel movements. Avulsions followed by channel incision form cobblefields in abandoned channels or other surfaces which are isolated from subsequent inundation and sediment deposition. These cobblefields embark on a different successional trajectory, which often includes conifer seedlings present in the initial cohort. Ultimately, whatever the initial trajectory, soils become productive due to soil conditioning by Alnus and the decomposition of other plant material. These biophysical complexities, interconnected patterns, and system-scale resilience are summarized in a multiple-pathway successional model that may be applicable to floodplain riparian forests throughout much of the Pacific coastal ecoregion.
TL;DR: This study uses detailed demographic data to determine the extent to which functional groupings, based on seedling recruitment and resprouting response to fire, capture the dynamics of postfire responses and early successional change in fire-prone ecosystems.
Abstract: This study uses detailed demographic data to determine the extent to which functional groupings, based on seedling recruitment and resprouting response to fire, capture the dynamics of postfire responses and early successional change in fire-prone ecosystems. Following massive wildfires in southern California, USA, we sampled chaparral and sage scrub vegetation in nested 0.1-ha plots from 90 sites for five postfire years. Prefire density of woody skeletons and cover and density of all postfire species were recorded. Functional types of postfire obligate seeder, facultative seeder, and obligate resprouter are broadly useful but fail to capture much of the dynamics of postfire succession in these shrublands. For the woody flora, stratifying these three regeneration modes by life-form captures important differences. Postfire obligate-seeding shrubs exhibit a single postfire seedling cohort whereas the faster growing suffrutescent species reach reproductive maturity by the second year and produce multiple seedling cohorts. Postfire obligate-resprouting shrubs reach reproductive maturity early but have very limited seedling recruitment in the early postfire years, whereas obligate-resprouting subshrubs flower the first year from resprouts and have seedling recruitment pulses in the second and subsequent postfire years. For the rich herbaceous flora, further subdivisions are needed to capture the range of variation. Herbaceous perennials are nearly all postfire obligate resprouters, and there are important demographic differences during early succession in different growth forms such as geophytes and rhizomatous grasses. Annuals lack resprouting ability and are postfire obligate seeders. Some exhibit extreme life-history specialization and are present only in the immediate postfire year(s). Others are highly specialized on fire but persist during early succession, and still others are opportunistic species widely distributed on open sites but can expand their populations during early succession.
TL;DR: This paper used 20-year time series from seven lakes to understand how dissolved inorganic carbon (DIC) and dissolved oxygen (DO) concentrations are controlled as a function of time scale.
Abstract: Dissolved inorganic carbon (DIC) and dissolved oxygen (DO) are commonly measured to compute metabolism of aquatic ecosystems. However, concentrations of DIC and DO depend on many factors in addition to ecosystem metabolism, such as water temperature, gas exchange with the atmosphere, abiotic chemical reactions, and inputs in precipitation, groundwater, and surface water. We used 20-year time series from seven lakes to understand how DIC and DO concentrations are controlled as a function of time scale. Diel cycles of both solutes are controlled primarily by metabolism, exchange with the atmosphere, and temperature. At seasonal and annual scales, metabolism is important, but physical processes associated with spring and autumn mixing, as well as solute loading from the watershed, have comparably large effects. At decadal scales, effects of metabolism are negligible. Controls of the two solutes diverge, with variance in DIC explained largely by solute inputs and variance in DO explained largely by water temperature. Like other indicators in many ecosystems, variability of DIC and DO is strongly scale dependent and associated with different drivers depending on the time scale of the analysis.
TL;DR: The effects of marine iguanas, sally lightfoot crabs, and fish on rocky-shore sessile organisms at two sites at Santa Cruz Island, Galapagos Islands, Ecuador, for 3–5 years during and after the 1997–1998 El Nino, using exclusion cages to separate the effects.
Abstract: We evaluated the effects of marine iguanas, sally lightfoot crabs, and fish on rocky-shore sessile organisms at two sites at Santa Cruz Island, Galapagos Islands, Ecuador, for 3–5 years during and after the 1997–1998 El Nino, using exclusion cages to separate the effects Plots exposed to natural grazing were dominated either by encrusting algae or by red algal turf and articulated corallines Algae fluctuated in response to El Nino in the following way During an early phase, crustose Gymnogongrus and/or red algal turf were dominant In the heart of El Nino, grazers had limited effects on algal cover but influenced algal sizes substantially Most algae (particularly edible forms) were scarce or declined, although warm-water ephemeral species (notably Giffordia mitchelliae) flourished, increasing diversity and overgrowing crusts Iguana mortalities were high, and crab densities low When normal conditions returned, warm-water ephemerals declined, crab densities rose, and grazers had significant but site-s
TL;DR: The data suggest that, despite their proximity, the dynamics of populations within the sites are being determined by small-scale rather than broad-scale spatial processes, and argue for a multitiered approach to the study of population variation.
Abstract: We used strong inference with Akaike's Information Criterion (AIC) to assess the processes capable of explaining long-term (1984-1995) variation in the per capita rate of change of mottled sculpin (Cottus bairdi) populations in the Coweeta Creek drainage (USA). We sampled two fourth- and one fifth-order sites (BCA (uppermost), BCB, and CC (lowermost)) along a downstream gradient, and the study encompassed extensive flow variation. Physical habitat availability varied significantly both within and among the sites. Sculpin densities in all sites were highly stable (coefficients of variation 5 0.23-0.41) and sampling variability was low (coefficients of variation 5 0.11-0.15). Population sta- bility was positively associated with habitat stability, and the only significant correlations of population parameters among sites involved juveniles. Sculpin densities were signifi- cantly higher in BCB than in CC. The data suggest that, despite their proximity, the dynamics of populations within the sites are being determined by small-scale (i.e., 30-50 m) rather than broad-scale spatial processes. Both AIC and Dennis and Taper analyses indicated that simple density dependence had the greatest ability to explain variation in r for all life-history classes in all sites (AIC, seven of nine cases; Dennis and Taper, nine of nine cases). Multiprocess models had little explanatory power. When adults were removed from two sites, juvenile sculpin shifted into microhabitats formerly occupied by adults. No shifts occurred in control sites. Consequently, it is likely that the patterns of density dependence observed in all three sites were a consequence of intraspecific competition for space. Our findings argue for a multitiered approach to the study of population variation, one that encompasses long-term monitoring, spatial variation, and experimental testing of potential mechanisms.
TL;DR: The authors used pollen assemblages from tree islands throughout the greater Everglades ecosystem to reconstruct the timing of tree island formation, patterns of development, and response to specific climatic and environmental stressors.
Abstract: Tree islands are centers of biodiversity within the Florida Everglades, USA, but the factors controlling their distribution, formation, and development are poorly understood. We use pollen assemblages from tree islands throughout the greater Everglades ecosystem to reconstruct the timing of tree island formation, patterns of development, and response to specific climatic and environmental stressors. These data indicate that fixed (teardrop-shaped) and strand tree islands developed well before substantial human alteration of the system, with initial tree island vegetation in place between 3500 and 500 calibrated years before present (cal yr BP), depending on the location in the Everglades wetland. Tree island development appears to have been triggered by regional- to global-scale climatic events at ;2800 cal yr BP, 1600- 1500 cal yr BP, 1200-1000 cal yr BP (early Medieval Warm Period), and 500-200 cal yr BP (Little Ice Age). These periods correspond to drought intervals documented in Central and South America and periods of southward displacement of the Intertropical Convergence Zone. The records indicate a coherence of climate patterns in both subtropical North America and the Northern Hemisphere Neotropics. Water management practices of the 20th century altered plant communities and size of tree islands throughout the Everglades. Responses range from loss of tree islands due to artificially long hydroperiods and deep water to expansion of tree islands after flow reductions. These data provide evidence for the rapidity of tree island response to specific hydrologic change and facilitate prediction of the response to future changes associated with Everglades restoration plans.
TL;DR: This work studied the thermal environment of the leaf-mining insect Phyllonorycter blancardella (Lepidoptera: Gracillariidae), which modifies both morphology and physiology of attacked apple leaf tissues to construct a mine inside which the entire larval development occurs.
Abstract: Physiology of ectothermic organisms depends on microclimate temperature. In some insect–plant relationships, the herbivore physically manipulates its proximate environment (i.e., plant tissues). However, little is known about the effects of this manipulation on the insect microclimate. We studied the thermal environment of the leaf-mining insect Phyllonorycter blancardella (Lepidoptera: Gracillariidae). This herbivore modifies both morphology and physiology of attacked apple leaf tissues to construct a mine inside which the entire larval development occurs. Spectral measurements showed that absorbance of mined leaf tissues differed from that of intact leaf tissues. Gas exchange measurements in mined leaf tissues demonstrated that responses of stomata to changes in climatic parameters were modified compared to intact leaf tissues. We built an energy budget model to predict the temperature within a mine given climatic variables, and measured parameters related to radiative absorption properties and to the e...
TL;DR: The form of density dependence in stage-specific mortality rates for three African ungulate populations for which data were available over a sufficiently wide range in abundance was examined, indicating that juvenile mortality was sensitive to various influences, some acting independently of density.
Abstract: The shape of the relationship between population growth rate and population density has important consequences for population dynamics. Past reviews have led to suggestions that, for large mammalian herbivores, the density-dependent response is curvilinear or abrupt in its onset above some threshold density, and that different demographic segments differ in their sensitivity to rising density. I examined the form of density dependence in stage-specific mortality rates for three African ungulate populations for which data were available over a sufficiently wide range in abundance: kudu in Kruger National Park, South Africa, and wildebeest in both Kruger and Serengeti National Park, Tanzania. Calf losses remained fairly high toward low-density levels, indicating that juvenile mortality was sensitive to various influences, some acting independently of density. The maximum population growth rate at low density was truncated by density-independent factors restricting recruitment success, while the slope of the...
TL;DR: The similarity of stimulant profiles in ancestral and novel host plants is consistent with the hypothesis that plant chemistry has played a role in the establishment of this host shift within the Papilio machaon group of swallowtail butterflies.
Abstract: Host shifts by herbivorous insects have contributed substantially to current patterns of association between insects and plants. Despite their evolutionary and agricultural interest, however, the plant traits that predispose insects to colonize some plants instead of others are poorly understood. To examine whether ancestral and novel hosts share similar chemical oviposition stimulants that would facilitate a host shift, we investigated a well-substantiated host shift within the Papilio machaon group of swallowtail butterflies. Papilio machaon aliaska uses three plant species as host plants. Cnidium cnidiifolium belongs to the family Apiaceae, the ancestral host-plant family of the P. machaon group. Artemisia arctica and Petasites frigidus, by contrast, belong to the family Asteraceae and were colonized relatively recently by this group of butterflies. Papilio machaon oregonius, a close relative of P. m. aliaska, feeds and oviposits exclusively on Artemisia dracunculus, also in the Asteraceae. We made polar and nonpolar extracts of all four host plants, conducted bioassays with P. m. aliaska and P. m. oregonius females to test for oviposition stimulants, and found that the polar extracts were the most active. Using high-performance liquid chromatography, we separated the polar extracts into three fractions and again conducted bioassays with P. m. aliaska and P. m. oregonius females. The fraction containing hydroxycinnamic acid (HCA) derivatives was the only active fraction for all plant species. We further separated the HCA fraction and found two sub-fractions that were active in all of the host-plant species. Co-chromatography indicated that several major constituents of the active fractions are shared between ancestral and novel hosts. In a secondary series of experiments, we investigated chemical fractions of a non-host plant, Artemisia frigida, and identified fractions of the A. frigida extract that contained oviposition deterrents and a fraction that contained oviposition stimulants for P. m. aliaska females. We conclude that the similarity of stimulant profiles in ancestral and novel host plants is consistent with the hypothesis that plant chemistry has played a role in the establishment of this host shift.
TL;DR: This work cross-dated a large number of increment cores and aligned the ring width data by pith date for accurate age constant assessments of growth over the past 150 years, and circumvented changes in growth trend associated with differences in physiological functioning during development.
Abstract: Despite experimental evidence showing that elevated C02 levels increase growth in most plants, the isolation of a signal consistent with anthropogenically caused increases in atmospheric C02 from the dendrochronological record has shown mixed results. Our extensive sets of tree ring data from the Ozark Mountains in Missouri showed that since 1850, Quercus velutina Lam., Quercus cocc?nea Muench., and Pinus echinata Mill, trees increased in stem growth coincidently with increases in atmospheric C02. Those long-term increases in radial growth appear unrelated to historical disturbance levels for the region, to long-term changes in relevant climatic variables, or to productivity of sites sampled for the purpose of creating a time sequence of tree ring growth. It is still unclear what the potential role of nitrogen deposition might have been for tree growth. We cross-dated a large number of increment cores and aligned the ring width data by pith date for accurate age constant assessments of growth over the past 150 years. Thus, we circumvented changes in growth trend associated with differences in physiological functioning during development, as well as the need for statistical detrending that removes an unknown degree of long-term environmental signal, the so called segment length curse that applies to standard dendrochronological investigations. When the positive relationship between C02 and ring width was examined at different ages, an ontogenetic decline in the rate of growth stimulation was found. Specifically, both the pooled Quercus spp. and P. echinata were characterized by a negative exponential pattern of response over a developmental sequence through age 50. Further knowledge of an intrinsic decline in C02 sensitivity with tree age or size such as this may be important for increased accuracy in estimating terrestrial carbon stocks across successional landscapes.
TL;DR: A new foraging model was developed that assumed a realistic decision-making rule for incompletely informed group foragers, and its performance was tested against existing models with different assumptions by comparing how well they reproduce the patterns observed in foraging White-fronted Geese.
Abstract: One important challenge of spatial ecology is to generate models linking individual behavior to population-level phenomena. Although animals often face great uncertainty regarding foraging patch quality, earlier models explaining the aggregation of animals have rarely specified how stable outcomes are achieved through individual decisions, especially under realistic assumptions for incompletely informed foragers. We developed a new foraging model that assumed a realistic decision-making rule for incompletely informed group foragers, and we tested its performance against existing models with different assumptions by comparing how well they reproduce the patterns observed in foraging White-fronted Geese (Anser albifrons). The assumptions in each of the four compared models were: (1) incompletely informed foraging with benefits of group foraging, which uses the expected gain rates for making decisions on diet choice, patch departure, and flock joining; (2) incompletely informed foraging without benefits of g...
TL;DR: A multisite capture–mark–resight analysis using 2050 Atlantic Puffins banded as chicks on four islands over 24 years in the Gulf of Maine, USA and Canada shows Colony-dependent survival probabil...
Abstract: Several weaknesses in our understanding of long-lived animal populations have persisted, mainly due to a prevalence of studies of a single local population at the expense of multisite studies. We performed a multisite capture–mark–resight analysis using 2050 Atlantic Puffins (Fratercula arctica) banded as chicks on four islands (colonies) over 24 years in the Gulf of Maine, USA and Canada. Within program MARK, encounter, apparent survival, pre-breeding movement (PBM; annual movements between colonies prior to breeding), and natal dispersal (ND) probabilities were modeled as functions of age, colony, and several covariates. Information-theoretic model selection criteria and estimated model effect sizes were used to identify important effects and select models to estimate parameters. Encounter probabilities were extremely variable (0.10–0.95) and declined annually starting six years after bands were applied, due to changes in resighting effort, and band wear, respectively. Colony-dependent survival probabil...
TL;DR: Overall, taxonomy and color were the traits most strongly associated with unpalatability and species appeared less constrained by predation and freer to forage for long periods on higher quality surface sediments or on other invertebrates at the sediment surface (thus, potentially influencing the distribution and abundance of other species).
Abstract: Marine worms are speciose and numerically prominent members of marine communities where they play critical roles in trophic interactions and in affecting biogeochemical cycles. Despite the ecological importance of this group, little is known about their palatability to, and defenses against, consumers. In addition, most studies of prey defenses in marine organisms have focused on overt, sessile species: few studies have investigated more mobile and behaviorally complex species that could potentially be integrating predator deterrents with refuge use and other escape behaviors. To increase our understanding of consequences of defensive traits among mobile marine prey, we surveyed the palatability of 81 species of worms from the Caribbean and warm-temperate western Atlantic. Thirty-seven percent of the species were unpalatable. Worms with differentially exposed body portions commonly defended exposed feeding appendages with chemical or structural deterrents, while palatable and undefended bodies remained sheltered within structural refuges. Unpalatable worms tended to be brightly colored and sedentary, exposed to epibenthic predators, and to occupy hard substrates. Palatable worms tended to be drab, to live in structural refuges from consumers, to be mobile, and to inhabit unconsolidated sediments. Overall, taxonomy (Sabellidae and Terebellidae) and color were the traits most strongly associated with unpalatability. Unpalatable species appeared less constrained by predation and freer to forage for long periods on higher quality surface sediments or on other invertebrates at the sediment surface (thus, potentially influencing the distribution and abundance of other species). In contrast, palatable species appeared more constrained by predation risk. They fed on lower quality subsurface sediments and foraged at times or locations where consumers were less active. These ecological patterns may be generalized to other soft-bodied prey, such as caterpillars, which show similar trends regarding palatability and lifestyle.
TL;DR: In laboratory flow-tank experiments, stream water collected near free-ranging adults induced hiding responses in 100% of the larvae tested, and the presence of TTX-sensitive cells within larval olfactory epithelium was confirmed by beh...
Abstract: Larvae of the California newt (Taricha torosa) exhibit striking predator-avoidance behavior, escaping to refuges in response to a chemical cue from cannibalistic adults. In laboratory flow-tank experiments, stream water collected near free-ranging adults induced hiding responses in 100% of the larvae tested. Solutions prepared by bathing adults (in field and laboratory) also evoked strong hiding behaviors. Insensitive to adult feeding status (fed or starved), and clearly not an excretory product, the chemical cue was released from adult skin (i.e., in swabs of adult backs, sides, and bellies). Tetrodotoxin (TTX) was found in skin swabs of adults and in bathwater at 1 × 10−7 mol/L using reversed-phase high-pressure liquid chromatography (HPLC). Concentrations of 1 × 10−7 to 1 × 10−9 mol/L TTX standard, and equivalent dilutions of bathwater, triggered hiding behaviors in larvae, with no subsequent sublethal toxicity. The presence of TTX-sensitive cells within larval olfactory epithelium was confirmed by beh...